Has it already been 15 years?  Yes, we are really that old now.  But I can promise you two things:  Everyone else is 15 years older as well, and the experience of seeing your classmates after 15 years will not be anything like you imagined it would be.  You will realize that everyone has grown up and become someone very different than you remember.  While you may be afraid that you will be confronted by that person you dread seeing, you will actually find most everyone quite happy to see you.  You may not realize it now, but the only regret you will have is if you do not come to the reunion.  You will leave thankful that you made the effort.  It puts the high school experience in a new light that has allowed for a completely new perspective that only comes with time.  To help alleviate your anxieties, please feel free to get in touch with fellow classmates.